This invention relates to couplers for optical fibers and more particularly to a coupler device for a concentric core fiber.
Essentially, a concentric core fiber has been developed and such fibers are available and have been manufactured by ITT Electro-Optical Products Division, Roanoke, Virginia. A concentric fiber consists of an inner core fabricated from a relatively low loss glass such as ultra-pure fused silica or a glass doped with germanium. The inner core is surrounded by an isolation layer or an isolation zone which is an annular region normally fabricated from a borosilicate glass. The purpose of the isolation zone is to prevent light which is propagated in the inner core from being coupled to an outer core which is an annular ring of glass surrounding the isolation zone. The outer core is surrounded by a substrate layer. The concentric core fiber enables one to provide dual transmission on a single conductor and hence, one can transmit different information on the inner core as compared to the outer core.
Due to the fact that the outer core is an annular structure, there has been considerable difficulty in the prior art in attempting to couple signals which are propagating in the outer core to suitable detecting devices so that the information transmitted in the outer core is available. Certain prior art systems employ complicated devices such as specially constructed mirrors, reflectors and masks as well as various other mechanical systems to retrieve the information propagating in an outer core of a concentric fiber.
It is therefore an object of the present invention to provide a simple and efficient coupler for a concentric core fiber.